Iron oxide grain coatings in red sandstones contain trace metals that are released upon dissolution of the coatings. Analyses by ICP-MS following acid leaching of the grain coatings show that the dissolved metals can constitute an ore-forming fluid, as hypothesized in models for sandstone13 hosted ore deposits. Mean compositions of 37 samples, mostly of Triassic to Devonian age, from across Britain and Ireland are 13.6 ppm copper, 2.9 ppm cobalt, 11.4 ppm vanadium and 0.4 ppm uranium. These contents at the basin scale are adequate to form the observed range of ore deposits 16 in red beds. The migration of hydrocarbons or brines can cause the dissolution of grain coatings, and contributes to controlling the distribution of ore deposits. Future measurements should test red beds derived from uplifted, mineralized plate margins, in which sandstones may be pre-loaded with ore metals.
Sandstone samples were kindly contributed by the Geological Survey of Northern Ireland, D. Halbert, R. Starkey, and L. Bullock. This work was partly supported by NERC grant NE/M010953/1. Electron Microscopy was performed with the help of J. Still in the ACEMAC Facility at the University of Aberdeen.
- Red sandstone
- red beds
- grain coatings
- ore fluid
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John Still (Manager)Geology and Geophysics
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